Flight Deck
Since the flight deck requires only a fraction of the air supply provided by the left
pack, most of the left pack output is routed to the mix manifold. Conditioned air for the flight
deck branches into several risers which end at the floor, ceiling and foot level outlets. Air
diffusers on the floor under each seat deliver continuous air flow as long as the manifold is
pressurized. Overhead diffusers are located on the flight deck ceiling, above and aft of the
No. 3 windows. Each of these outlets can be opened or closed as desired by turning a
slotted adjusting screw. There is also a dual purpose valve behind the rudder pedal of each
pilot. These valves provide air for warming the pilots' feet and for defogging the inside of the
No. 1 windshields. Each valve is controlled by knobs located on the Captain's and First
Officer's panels.
Passenger Cabin
The passenger cabin air supply distribution system consists of the mix manifold, sidewall
risers, and an overhead distribution duct. Sidewall risers go up the right and left walls of the
passenger cabin to supply air to the overhead distribution duct. The overhead distribution
duct routes conditioned air to the passenger cabin. It extends from the forward to the aft end
of the ceiling along the airplane centerline and also supplies the sidewall diffusers.
Recirculation Fan
The recirculation fan system reduces the air conditioning system pack load and the engine
bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to
the forward cargo bay where it is filtered and recirculated to the mix manifold. The fans are
driven by AC motors. Each recirculation fan operates only if the respective RECIRC FAN
Switch is selected to AUTO. In flight, the left recirculation fan operates if both packs are
operating unless either PACK switch is in HIGH.
